A group of scientists recently stumbled across a remarkable but eerie sight while diving at the Hannibal Bank Seamount off the coast of Panama. Beneath a shifting mist of sea sediment was a massive cloud of crabs, scuttling along by the thousands at the bottom of the sea. Researchers are baffled about what would make these crabs behave this way.

According to the Woods Hole Oceanographic Institution, the research team was studying biodiversity in the waters off Panama when they discovered the incredible cloud of crabs, a sight that biologist Jesús Pineda called “mesmerizing.” In the video above, you can see the crabs swarming in countless numbers around the 1:10 mark. Though they are red crabs, the creatures appear to be a ghostly gray behind the murky veil of sediment on the sea floor. What results is an almost skin-crawling image of thousands of ten-legged critters drifting slowly through the low-oxygen waters.

“When we dove down in the submarine, we noticed the water became murkier as we got closer to the bottom,” said Pineda, lead author of the paper. “There was this turbid layer, and you couldn’t see a thing beyond it. We just saw this cloud but had no idea what was causing it. At first, we thought they were biogenic rocks or structures. Once we saw them moving, swarming like insects, we couldn’t believe it.”

While the cloud of crabs may seem like nothing more than a fascinating bit of footage, the scientists who discovered them claim the crabs’ behavior is actually a natural anomaly that should be investigated more closely.

“Nothing like this has ever been seen, where we have this very dense swarm at the bottom. We have no idea why they might be doing this.”

Scientists sequenced the DNA of the animals in the cloud of crabs and determined them to be the species Pleuroncodes planipes. While this isn’t an uncommon ocean creature, the gargantuan cloud of crabs seen in the video was located in an area to which the species never used to venture. The discovery marks the southernmost spot that the red crabs have ever been found.

“No one had ever found this species that far south,” Pineda explained. “To find a species at the extreme of their range and to be so abundant is very unusual.”

According to the Guardian, Pineda made absolutely sure that this cloud of crabs was an unrecorded phenomenon by searching through many volumes of scientific research about sea animals that live on the ocean floor. He found that not only was it unusual for the crabs to swarm in such large groups, but the cloud of crabs was also found 1,200 feet below the surface, where the water has so little oxygen that most organisms can’t survive.

Pineda and his team of researchers published the discovery of the cloud of crabs in the journal PeerJ. The scientists noted that global warming could be the cause of the strange behavior. Climate change could have destroyed the ecosystems on which the crabs depended, forcing them to move to new areas to find food.

“High density aggregations and a swarm of red crabs were associated with a dense turbid layer 4–10 m above the bottom,” says the findings. “Crab density peaked in the middle of the patch, a density structure similar to that of swarming insects.”

It might be the similarity to a swarm of insects that makes the cloud of crabs so unsettling in the deep sea footage. Do you find the video fascinating or creepy?